Video synchronizers are used in television studios, for example, for synchronizing various video sources (e.g., cameras, VTR's etc.) to a common standard studio timing signal source ("House Sync"). Commercial (broadcast quality) synchronizers (e.g., frame stores) are too costly, as a practical matter, for use in synchronizing consumer video products such as disc or tape players with other sources such as home computers or computer controlled video games. As is well known, such video sources do not generally provide video output signals which comply with NTSC standards as to line rates and color subcarrier frequency tolerances.
One approach to the problem of providing video synchronization of "consumer" video products is described in U.S. Pat. No. 4,346,407 entitled "APPARATUS FOR SYNCHRONIZATION OF A SOURCE OF COMPUTER CONTROLLED VIDEO TO ANOTHER VIDEO SOURCE" which issued to Baer et al. on Aug. 24, 1982. The Baer et al. system desirably avoids the use of relatively expensive frame or line stores. In the Baer et al. system, synchronization of a source of computer controllable video (e.g., a home computer or video game) to another video source (e.g., a disc or tape player) is achieved by providing clock pulses for the source of computer controlled video at some multiple of the horizontal synchronization frequency of the other video source to obtain frequency coherence and by detecting phase incoherence between the signals from the two sources and in response thereto causing the clock pulses to cease for a predetermined period to allow the source of computer controlled video to "slip" sync to obtain phase coherence.
The Baer et al. system achieves its general objective of locking computer generated video signals to the source of externally generated video without the use of conventional frame or line stores. This desirable benefit is not obtained, however, without certain sacrifices. In particular, Baer et al. states that one of the phase locked loop components of the exemplary system they propose requires up to 910 fields to achieve phase lock. This corresponds to a lock-up time of about 15 seconds.